The invention relates to a control program for controlling a source of electromagnetic radiation with which a cross-linking in the eye tissue of the patient is implemented by means of a photosensitiser introduced into the tissue, and also to a process for producing such a control program, and to a process for ascertaining whether a patient is suitable for an ophthalmological treatment involving cross-linking of eye tissue by means of electromagnetic radiation and a photosensitiser.
The human eyeball is bounded by the outer tunic of the eyeball. By virtue of the intraocular pressure, the collagen-containing outer tunic of the eyeball is tightened and imparts an approximately spherical shape to the healthy eyeball. In the posterior eyeball region the outer tunic of the eyeball consists of the white sclera. Located in the anterior region is the cornea, which is transparent to visible light.
Deformations of the outer tunic of the eyeball can be the cause of defective vision. For example, one form of short-sightedness, axial myopia, can be the consequence of a scleral increase in the length of the eyeball. A surface of the cornea shaped as an ellipsoid can result in a form of astigmatism that is also designated as corneal distortion. Another disease of the cornea is designated as keratoconus. In the case of keratoconus, a progressive thinning and conical deformation of the cornea of the eye occur as a consequence of a pathological softening of the cornea. With the increasing bulging, the cornea becomes thinner below the centre. It may rupture and form a scar. This reduces visual acuity permanently. The causes of keratoconus are largely unknown even today. It occurs with increased frequency within a family, which speaks, inter alia, for a genetic predisposition. Atopic disorders such as allergic diseases constitute a further risk factor for the genesis of a keratoconus.
The conventional therapy for an advanced keratoconus provides for removing the diseased cornea and replacing it with an allogeneic graft. Such an operation is, however, an organ transplant, with the associated risks and complications. An appropriate visual faculty is frequently obtained only about two years after the operation. In addition, the transplantation of the cornea in the case of keratoconus mostly affects young persons, which is why the transplant has to function perfectly over a period of decades.
A therapy for keratoconus that is improved in contrast to this stabilises the cornea by cross-linking. The treatment permits a photochemical, non-tissue-ablating stabilisation or change of the biomechanical and biochemical properties of the cornea. The therapeutic principle is also applicable to other affected regions of the eye. A photosensitiser solution is introduced into the eye tissue to be changed and is exposed to a primary radiation. Electromagnetic radiation within the wavelength range from approximately 300 nm to 800 nm (UV-A radiation or visible light) is employed as primary radiation.
Appropriate apparatuses for treating the outer tunic of the eyeball are known from documents WO 2007/128581 A2 and WO 2008/000478 A1.
An apparatus according to WO 2007/128581 A2 serves for strengthening the sclera located in the posterior portion of the eye. In this case the primary radiation can act on the sclera through the interior of the eye or through pads resting against it from outside. By means of a photomediator or photosensitiser, a cross-linking is brought about in the sclera. As a result, a growth of the sclera is counteracted and a progression of the axial myopia is prevented.
Printed publication WO 2008/000478 A1 describes an irradiation system for biomechanical stabilisation of the cornea. Here too, in conjunction with a photosensitiser a cross-linking can be brought about on the cornea. The irradiation system offers the possibility of treating specific diseases such as keratoconus.
The change of the form and/or of mechanical properties of eye tissue, in particular of the cornea and generally of the sclera, by means of an introduced photosensitiser and electromagnetic radiation is well-known as such in the state of the art, in particular as mentioned above. With regard to the chemical composition of the photosensitiser, reference is made to the state of the art, also with regard to the type of electromagnetic radiation employed, in particular the suitable wavelengths in conjunction with certain photosensitisers.
However, complex dependences conflict with a routine use of cross-linking therapy on the eye tissue. The relationships between the doses employed and the effect thereof in the eye tissue are highly diverse. By way of dose in this sense there enter into consideration, in particular, the electromagnetic radiation with regard to its intensity as well as its distribution in space and time; the photosensitiser employed with regard to its chemical structure, concentration, and action in space and time.
The effects of different doses of these parameters on and in the eye tissue of a patient are very highly dependent on properties (measurement data) with reference to the patient. In this connection it is to be taken into account, in particular, that the effect of the cross-linking implemented with the radiation and the photosensitiser may also be undesirable and may go so far as to damage the eye tissue or the functioning of the eye.
The object underlying the invention is to make processes and control programs available with which an assessment of the effect of a cross-linking can be estimated as reliably as possible already in the run-up to a possible ophthalmological intervention.